Dopant and Defect Doubly Modified CeO2/g-C3N4 Nanosheets as 0D/2D Z-Scheme Heterojunctions for Photocatalytic Hydrogen Evolution: Experimental and Density Functional Theory Studies

Exploring novel 2D heterojunction photocatalysts with a wide spectral response and high active site exposure has been a huge challenge. A small-sized catalyst with high dispersibility has been considered an ideal model for maximizing active sites and increasing atomic efficiency. Herein, the 0D/2D Z-scheme heterojunction was designed by in situ solvothermal and subsequent calcination in air by integrating dopant and defect doubly modified CeO2 nanodots and g-C3N4 nanosheets (CNNS). Ultrafine cobalt-doped CeO2 nanodots (≈4 to 5 nm) with enriched oxygen vacancies (Co-CeO2–OVs) were uniformly and tightly anchored on the surface of CNNS to form a heterojunction. The density functional theory (DFT) calculations confirmed that cobalt dopants and oxygen vacancies form impurity energy states at the top of a valence band, thus narrowing the band gap. The optimized 0D/2D heterojunction showed a remarkable hydrogen production rate of ∼203.6 μmol/h, which was approximately 4.9- and 30.8-fold higher than that of CNNS (∼41.2 μmol/h) and CeO2 (∼6.6 μmol/h), respectively. Moreover, a large quantum yield of ∼8.94% was achieved at 420 nm. The 0D/2D heterojunction with a larger intimate area provided abundant reactive active sites and strong electron interactions to excite photogenerated carrier dynamics, and the doping and defect engineering could expand the light response range by regulating the electronic band structure. Strong evidence provided by experimental results and DFT calculations proved the Z-scheme charge transfer pathway. This work not only provided a novel approach to integrate 0D nanodots and 2D nanosheets for the formation of intimate Z-scheme heterointerfaces but also deepened the understanding of the dopant–defect synergistic modification to optimize the band structure and electronic structures for high-efficient solar energy capture and conversion.